Drill bits with composite cutting elements

Abstract: A novel form of drill bit is disclosed. The bit (30) comprises a bit body having a leading face (32) and gauge surface (44, 46). Cutting inserts (32, 34, 36) are set into the bit body, each cutting insert being in the form of a segment of a composite PCD (polycrystalline diamond) or PCBN (polycrystalline cubic boron nitride) composite. Thus each insert has a PCD or PCBN compact (40) carried by a carbide backing (42). The PCD or PCBN compact of each insert is exposed at the leading face or at the gauge surface to perform an axial cutting or gauge maintenance function during drilling.

Description: This invention relates to drill bits, including coring bits used to extract sample cores from the earth, and non-coring bits used to drill holes into the earth. A known coring bit has a tubular steel body with a leading end adapted to perform a cutting operation and a trailing end adapted to be connected to the leading end of a tubular drill string. The leading edge of the bit typically carries abrasive particles. Commonly used non-coring bits usually have abrasive buttons or cutting inserts set into their leading or working face. An object of the present invention is to provide novel forms of drill bit for coring applications. EP-A-0 506 238 discloses a drill bit in accordance with the preamble of claim 1. According to the present invention there is provided a coring drill bit comprising a tubular bit body having a leading face, an inner gauge surface and an outer gauge surface, and a series of cutting inserts set into the bit body, the cutting inserts being in the form of segments which are cut from slices of composite PCD or PCBN compacts which are of flat proportions, characterised in that each cutting insert includes a PCD or PCBN compact carried by a carbide backing which is set into the bit body, some of the cutting inserts being arranged with their PCD or PCBN compacts exposed at the leading face of the bit and extending in a radial direction across the leading face from the inner gauge surface to the outer gauge surface, some of the cutting inserts being arranged with their PCD or PCBN compacts exposed at the inner gauge surface and extending axially along the inner gauge surface, and some of the cutting inserts being arranged with their PCD compacts exposed at the outer gauge surface and extending axially along the outer gauge surface. In one embodiment, the cutting inserts may be identical but arranged at different orientations to provide for exposure of PCD or PCBN compacts at the leading face and inner and outer gauge surfaces. The cutting inserts may be arranged singly or in clusters of three inserts each. In the latter case, the three cutting inserts in each cluster are arranged for their PCD or PCBN compacts to be exposed at the leading face and inner and outer gauge surfaces respectively. The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which: Figure 1 illustrates diagrammatically how a blank is sliced up in the production of the cutting inserts used in the drill bit of Figures 3 to 8; Figure 2 shows a side view of the blank seen in Figure 1; Figure 3 shows an axial view on the face of a coring drill bit according to the invention; Figure 4 shows a cross-section at the line 4-4 in Figure 3; Figure 5 shows an axial view on the face of another embodiment of coring drill bit according to the invention; Figure 6 shows an exploded perspective view of a cutting insert assembly as used in the Figure 5 bit; and Figure 7 shows the cutting insert assembly of Figure 6 in assembled form. Figures 1 and 2 illustrate a blank 10 from which a great number of cutting inserts for use in drill bits can be produced in accordance with the invention. The blank in this case is a SYNDITE (trade mark) blank which is of generally circular shape and which is manufactured by the applicant. The SYNDITE (trade mark) blank is a composite PCD compact consisting of a thin PCD compact 12 bonded to a tungsten carbide backing 14, and it typically has a thickness 16 of about 8mm. To produce cutting inserts for use as described below, the blank 10 is cut into slices 18 along slice lines 20 which are at right angles to the major surfaces 22 and 24 of the blank. The SYNDITE blank 10 may have a substantial nominal diameter 28, typically of up to 70mm, which determines the maximum possible length dimension of a cutting insert that can be produced using the slicing technique just described. In most cases, however, the slices 18 are then cut up lengthwise to form cutting inserts of appropriate dimension for use in a drill bit, as described below. Figure 3 shows an axial view on the leading face of a coring drill bit designed for drilling into rock formations and for extracting solid cylindrical cores from those formations, generally for the purpose of geological analysis or in prospecting operations. As seen in this Figure, the body 30 of the coring bit is of hollow cylindrical shape, so that the leading face 30 has an annular configuration. Cutting inserts 34, 36 and 38 are set into angularly spaced, radially orientated recesses in the face. The inserts 34, 36 and 38 are identical and are in the form of segments cut from slices of a blank 10, as described above. Each of the inserts has a PCD compact 40 bonded to a tungsten carbide backing 42. As will be clear from Figure 3, the inserts 34 are set into the relevant recesses in such a manner that their PCD compacts 40 are exposed slightly above face 32 and extend from the inner gauge 44 of the bit body to the outer gauge 46 thereof. During drilling, with the drill bit rotating about its axis and urged in the axial direction, the cutting inserts 34 will perform an axial cutting action. The two cutting inserts 36 are set into the relevant recesses with their PCD compacts flush with the inner gauge 44. The two cutting inserts 38 are reversed with respect to the cutting inserts 36 and are set into the relevant recesses so that their PCD compacts are flush with the outer gauge 46. During drilling, the inserts 36 and 38 serve to maintain the inner and outer gauges cut by the inserts 34. Since they are not intended to perform any appreciable axial cutting action, this being the task of the inserts 34, the inserts 36 and 38 can be set back axially in the face 32 relative to the inserts 34. Figure 5 shows a view similar to that of Figure 3 of another embodiment of coring drill bit. In this case, axial cutting as well as inner and outer gauge maintenance is performed by four cutting insert clusters. A typical cutting insert cluster 50 is illustrated in Figures 6 and 7. As will be evident from these Figures, the assembly 50 consists of three separate cutting inserts 54, 56 and 58 arranged side-by-side with one another. The inserts 54, 56 and 58 correspond in shape and orientation to the inserts 34, 36 and 38 respectively of the preceding embodiment, with the inserts 54 performing axial cutting and the inserts 56 and 58 maintaining the inner gauge and outer gauges respectively. In each embodiment, the inserts are typically anchored by brazing them into in the relevant recesses in the bit body, although other suitable fixing methods such as clamping can also be used. In each case, typical cutting insert dimensions would be as follows: Thickness 1mm upwards Height 5mm to 10mm Width (length) 5mm to 40mm In the case of inserts using PCD compacts, the thickness of the diamond layer will typically be in the range 0,7mm to 1,5mm. It is believed that a drill bit incorporating cutting inserts as described with reference to Figures 3 to 7 will be suitable for drilling in soft to medium rock formations such as clay, sandstone and shale. It should also be noted that instead of a PCD compact providing the cutting tip of the cutting insert in the various embodiments of the invention, PCBN (polycrystalline cubic boron nitride) could be used. Although reference is made in this specification to the slicing of a single PCD or PCBN composite compact or blank to produce the cutting inserts which are then used in the drill bit, it will readily be appreciated that in practice not all of the cutting inserts in one drill bit will necessarily emanate from the same original composite compact. The invention also embraces the situation where cutting inserts emanating from different composite compacts are used in the same drill bit. Also, while specific mention has been made of a SYNDITE blank as the source for the cutting elements, it should be noted that the invention is in no way limited to the use of this particular form of blank. In other embodiments, different PCD or PCBN composite compacts could be used as a source for the cutting inserts.

Claims: A coring drill bit comprising a tubular bit body (30) having a leading face (32), an inner gauge surface (44) and an outer gauge surface (46), and a series of cutting inserts (54, 56, 58) set into the bit body, the cutting inserts being in the form of segments which are cut from slices (18) of composite PCD or PCBN compacts (10) which are of flat proportions, characterised in that each cutting insert includes a PCD or PCBN compact (40) carried by a carbide backing (42) which is set into the bit body, some of the cutting inserts (54) being arranged with their PCD or PCBN compacts exposed at the leading face of the bit and extending in a radial direction across the leading face from the inner gauge surface to the outer gauge surface, some of the cutting inserts (56) being arranged with their PCD or PCBN compacts exposed at the inner gauge surface and extending axially along the inner gauge surface, and some of the cutting inserts (58) being arranged with their PCD compacts exposed at the outer gauge surface and extending axially along the outer gauge surface. A coring drill bit according to claim 1 characterised in that the cutting inserts are arranged in clusters (50) of three inserts each, the cutting inserts in each cluster being similar to one another but arranged at different orientations so as to be exposed at the leading face, at the inner gauge surface and at the outer gauge surface respectively.

Inventors: CLARK IAN ERIC, CLARK, IAN ERIC
Applicants: DE BEERS IND DIAMOND, DE BEERS INDUSTRIAL DIAMOND DIVISION (PROPRIETARY) LIMITED
Application year: 1994
Main classification: E21B10
IPC codes: E21B10, B27B33, B28D1, B23P15